This invention relates to web transport apparatus and, more particularly, to the automatic threading by means of a flexible threading band of a web, contained in a cassette, along an external web transport path past a web utilization station.
Web-utilization devices, such as magnetic tape recorders, frequently operate with long strips of web wound on supply and take-up reels in a cassette. The utilization device must extract the web from the cassette in order to move it along a transport path within the device past one or more web utilization stations. Thus, for example, a helical scan magnetic tape recorder typically records and reproduces information on magnetic tape which is wound on supply and take-up reels contained in a cassette which is removable from the recorder. The tape transport path within the recorder is complex and may include, for example, several tape guides, tape-tension mechanisms, drive capstans, fixed magnetic heads and a rotary head scanner about which the tape is wrapped at a helix angle relative to the plane of rotation of the rotary heads.
Various techniques have been proposed for automatically threading magnetic tape from cassettes along the tape path of the recorder. The vast majority of these techniques utilize mechanical guides and posts which are manipulated by means of complex slides and linkages to extract the tape from a cassette and to configure it to the tape recorder transport path. Examples of such mechanical threading techniques are disclosed in the following patents: U.S. Pat. No. 3,688,055, issued Aug. 29, 1972, entitled GUIDE PLATE FOR USE WITH TAPE RECORD/PLAYBACK MECHANISM; U.S. Pat. No. 4,017,897, issued Apr. 12, 1977, entitled MAGNETIC TAPE GUIDE HAVING A TAPPERED ROLLER AND AN ADJUSTABLE CONTOURED EDGE; U.S. Pat. No. 4,170,787, issued Oct. 9, 1979, entitled TAPE RECORDING/REPRODUCING APPARATUS, PARTICULARLY FOR OPERATION WITH VIDEO TAPE CASSETTES; U.S. Pat. No. 4,191,979, issued Mar. 4, 1980, entitled DEVICE FOR EXTRACTING AND POSITIONING - VIDEO TAPE FROM A CASSETTE TO AROUND A SLIT HEAD DRUM; U.S. Pat. No. 4,322,761, issued Mar. 30, 1982, entitled TAPE GUIDE IN A HELICAL SCAN CASSETTE RECORDER; U.S. Pat. No. 4,264,937, issued Apr. 28, 1981, entitled MAGNETIC TAPE GUIDE ALIGNMENT DEVICE; U.S. Pat. No. 4,166,283, issued Aug. 28, 1979, entitled SELF-THREADING HELICAL SCAN VIDEO CASSETTE RECORDER; U.S. Pat. No. 3,871,025, issued Mar. 11, 1975, entitled TAPE LOADING SYSTEM FOR AUTOMATICALLY WITHDRAWING A TAPE FROM A CASSETTE AND ENGAGING THE TAPE WITH A RECORDING AND/OR REPRODUCING HEAD; U.S. Pat. No. 4,620,245, issued Oct. 28, 1986, entitled TAPE LOADING APPARATUS FOR USE IN A RECORDING AND/OR REPRODUCING APPARATUS OF THE ROTATING HEAD KIND; and U.S. Pat. No. 4,672,476, issued June 9, 1987, entitled MAGNETIC TAPE RECORDING AND/OR REPRODUCING APPARATUS.
The mechanical tape-threading devices disclosed in these patents have the following disadvantages: (1) the devices are complex, expensive and space-consuming; (2) the many moving parts of the device are subject to mechanical breakdown, requiring repair; (3) the mechanical device is noisy during threading and unthreading and not suitable for applications requiring quiet operation; (4) the device subjects the tape to wear, damage and stretching; (5) the movable guides which establish the helix angle of wrap of tape around the rotary head scanner may be misaligned, thus causing mistracking of a reproduce head on recorded tracks and consequent poor signal reproduction; (6) the path of the tape in a helical scan recorder utilizes both movable guides and fixed capstans which require severe manufacturing tolerances, thus resulting in high manufacturing cost to achieve high reproduce/record signal quality and interchangeability of tape cassettes.
In order to minimize the disadvantages of mechanical tape-threading devices, a less complex threading technique has been proposed in commonly assigned U.S. Pat. No. 4,772,969, issued Sept. 20, 1988, entitled "EXPANDABLE LOOP" METHOD OF AND APPARATUS FOR AUTOMATICALLY THREADING A WEB MATERIAL TO THREAD TAPE FROM A CASSETTE INTO THE TRANSPORT PATH OF A MAGNETIC TAPE RECORDER BY MEANS OF AN AIR EVACUATION TECHNIQUE. As disclosed in this patent, a vacuum source establishes an air pressure gradient to controllably pull tape, spanning the supply and take-up reels of a cassette, toward the transport elements of a magnetic tape recorder. The tape forms an expandable loop which ultimately takes the shape of the tape transport path. The pneumatic-threading technique of the latter patent provides a simplified and less expensive design than known mechanical threading systems. Moreover, tape threading is significantly faster and more gentle, with less likehood of damage or tearing to the tape. Although the latter technique is suitable for the purposes for which it was intended and solves many of the problems of mechanical-threading techniques, there may be applications where space will not permit use of a pneumatic system because of the amount of space consumed by an air evacuation system.